I know it started being offered in 08. When did it cease as a non special order color?

 

This website was posted in the other forum in the 991 section by Suzy. It's in German, but maybe you can use translate to get the info you need. I'd check myself but I'm on my phone:

http://www.elferclassic.de/technik/farben/plack_weiss.php

 

According to that site, ruby red pearl was 2007-2009, ruby red metallic was '09-12. My paint code is pearl, so I guess the answer is '09.

 

Also, keep in mind since that site in in German, it presumably reflects paints available in Germany, not US.